The distance a golf ball travels when struck by a golf club is determined in large part by club head speed at the point of impact with the golf ball. Club head speed in turn can be affected by the wind resistance or drag provided by the club head during the entirety of the swing, especially given the large club head size of a driver. The club head of a driver or a fairway wood in particular produces significant aerodynamic drag during its swing path. The drag produced by the club head leads to reduced club head speed and, therefore, reduced distance of travel of the golf ball after it has been struck.
Air flows in a direction opposite to the golf club head's trajectory over those surfaces of the golf club head that are roughly parallel to the direction of airflow. An important factor affecting drag is the behavior of the air flow's boundary layer. The “boundary layer” is a thin layer of air that lies very close to the surface of the club head during its motion. As the airflow moves over the surfaces, it encounters an increasing pressure. This increase in pressure is called an “adverse pressure gradient” because it causes the airflow to slow down and lose momentum. As the pressure continues to increase, the airflow continues to slow down until it reaches a speed of zero, at which point it separates from the surface. The air stream will hug the club head's surfaces until the loss of momentum in the airflow's boundary layer causes it to separate from the surface. The separation of the air streams from the surfaces results in a low pressure separation region behind the club head (i.e., at the trailing edge as defined relative to the direction of air flowing over the club head). This low pressure separation region creates pressure drag. The larger the separation region, the greater the pressure drag.
During a golfer's backswing, the ball striking face, which starts at an address position, twists outwardly away from the golfer (i.e., clockwise when viewed from above for a right-handed golfer) due to rotation of the golfer's hips, torso, arms, wrists and/or hands. During the downswing, the ball striking face rotates back into the point-of-impact position. During the downswing, the golf club head may be rotated by about 90° or more around the longitudinal axis of its shaft during the 90° of downswing prior to the point of impact with the golf ball. In fact, the heel/hosel region of the club head leads the swing during a significant portion of the entire downswing and the ball striking face only leads the swing at (or immediately before) the point of impact with the golf ball.
Additionally, during the final 90° portion of the downswing, the club head may be accelerated to approximately 65 miles per hour (mph) to over 100 mph, and in the case of some professional golfers, to as high as 140 mph. As the speed of the club head increases, typically so does the drag acting on the club head. Thus, during this final 90° portion of the downswing, as the club head travels at speeds upwards of 100 mph, the drag force acting on the club head could significantly retard any further acceleration of the club head.
The summation of the drag forces during the entire downswing provides the total drag work experienced by the club head. Calculating the percent reduction in the drag work throughout the course of the entire downswing can produce a very different result than calculating the percent reduction in drag force at the point of impact only. Thus, club heads that have been designed to reduce the drag of the head at the point of impact, or from the point of view of the club face leading the swing, may not function well to reduce the drag during other phases of the swing cycle, such as when the heel/hosel region of the club head is leading the downswing. The drag-reducing structures described below provide various means to reduce the total drag, not just reducing the drag at the point-of-impact. Reducing the total drag of the club head would result in improved club head speed and increased distance of travel of the golf ball.
It would be desirable to provide a golf club head that reduces or overcomes some or all of the difficulties inherent in prior known devices. Particular advantages will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view of the following disclosure of the invention and detailed description of certain embodiments.